This invention relates to a process for polymerizing an olefin with a supported catalyst. The supported catalyst contains an aromatic solvent and is made from an organometallic complex comprising a Group 3 to 10 transition metal and a bridged indenoindolyl ligand bonded to the metal. The process gives polyolefins with improved flow.
Many olefin polymerization catalysts are known, including conventional Ziegler-Natta catalysts. While these catalysts are inexpensive, they exhibit low activity and are generally poor at incorporating xcex1-olefin comonomers. To improve polymer properties, single-site catalysts, in particular metallocenes are beginning to replace Ziegler-Natta catalysts.
Catalyst precursors that incorporate a transition metal and an indenoindolyl ligand are known. U.S. Pat. Nos. 6,232,260 and 6,451,724 disclose the use of transition metal catalysts based upon indenoindolyl ligands, but have no examples using supported catalysts. While they mention that supported catalysts may be used, little information is given about the preparation of the supported catalysts. No indication of using an aromatic solvent containing supported catalyst is given.
WO 01/53360 discloses open architecture indenoindolyl catalysts that may be supported. In the single example (Example 8) preparing a supported catalyst, a solution of the catalyst is added to a polyethylene support in 3 aliquots, and after each addition, the solvent is evaporated under vacuum.
U.S. Pat. No. 6,559,251 discloses a process for polymerizing olefins with a silica-supported, indenoindolyl Group 4-6 transition metal complex having open architecture. Volatiles are removed in the preparation of the supported catalyst. The polymers prepared with the silica supported open architecture complex have extremely high molecular weight, even when the polymerization is done in the presence of hydrogen.
U.S. Pat. No. 6,211,311 prepares supported catalysts containing heteroatomic ligands, but dries the supported catalysts under vacuum before use. U.S. Pat. No. 6,541,583 discloses a process for polymerizing propylene in the presence of a Group 3-5 transition metal catalyst that has two non-bridged indenoindolyl ligands. None of the examples uses a supported catalyst. They state that the catalyst can be immobilized on a support but give no process details and do not mention the use of an aromatic solvent.
Pending application Ser. No. 10/123,774, filed Apr. 16, 2002, discloses a process for polymerizing ethylene in the presence of a supported Group 3-10 transition metal catalyst that has two bridged indenoindolyl ligands. In each of the examples showing supported catalysts (Examples 7-12), volatiles are removed.
Despite the considerable work that has been done with catalysts based upon indenoindolyl ligands there is a need for improvement, especially with regard to regulation of flow properties. For many processing techniques, such as injection molding, an increase in flow improves the ability to melt process the polyolefin. In particular, bridged indenoindolyl catalysts generally have relatively low hydrogen sensitivity. In other words, polymer molecular weight is not easily reduced by adding hydrogen in the polymerization process. Ideally, the hydrogen sensitivity of bridged indenoindolyl catalysts could be improved, and a process could be developed that provides more control over polymer flow properties.
The invention is a process for making polyolefins with improved flow properties. An organometallic complex and an activator are combined with a support material in the presence of an aromatic solvent to prepare a supported catalyst containing the aromatic solvent. The organometallic complex comprises a Group 3 to 10 transition metal and a bridged indenoindolyl ligand that is bonded to the transition metal. The supported catalyst containing the aromatic solvent is mixed with an olefin, and the olefin is polymerized in the presence of hydrogen. The resulting polyolefins have improved flow properties.